Artificial Selection

  1. Sexual Selection

    1. a special case when selection is exerted by members of your own species in ways that affect reproductive success

    2. 2 forms

      1. male on male competition over access to mates and resources

      2. females choose higher quality males

    3. choice by females drives evolutionary elaboration of the male trait

      1. over time female choosiness and the male trait become genetically linked due to selection acting on both traits

  2. Artificial Selection in corn

    1. the progenitor of corn is teosinte

      1. an ancestor or original source of something

    2. the transformation of corn was achieved by modifications of only 5 genes of large effect

  3. Artificial Selection in dogs

    1. belyaev experiment

      1. human choose which fox got to breed based on how friendly they where to humans

      2. by 1979 foxes exhibited less fear over time

        1. evolved morphological traits like floppy ears, curly tails and spotted coats

  4. natural selection in beach mice

    1. Harvard university studies the evolution of color pattern in field mice

    2. Oldfield Deer mouse

      1. live in loosely packed sandy or clay soils where they can dig their burrows

      2. have a dark brown dorsal coat, light grey belly and a striped tail

    3. Beach mouse

      1. live on white sand with sparse vegetations

      2. have a light colored dorsal coat and no pigment on their face, belly and tail

  5. Understanding Natural Selection

    1. ultimate explanation

      1. looks at the big picture of how a trait improves an organisms chances of passing on its gene

      2. biologists try to understand WHY certain traits help organisms survive and reproduce better in their environment

    2. proximate explanations

      1. focuses on the immediate cause of a trait

      2. biologists study how traits appear in living things

      3. if a scientists wants to know why some mice have light fur and others have dark fur they would look at things like..

        1. genes: what DNA changes cause the fur to be light or dark

        2. development: how does the fur color develop as the mouse grows

        3. physiology: what body processes create the pigments that give the fur its color

  6. How is fur coloration determined

    1. each hair grows from a hair follicle and melanocytes at the base of each follicle produce pigments

    2. variation is determined by two pigments, pheomelanin and eumalanin

    3. mammalian pigments

      1. emulanin

        1. produces dark colored hair, brown to black

      2. pheomalnin

        1. produces light colored hairs, blond to red

  7. Genes affecting hair color

    1. melanocrotin-1 receptor (mc1r)

    2. agouti

    3. General model

      1. genes code for mc1r, melanocytes stimulating hormone (MSH) and agouti protein

      2. MSH signals for the production of eumelanin

      3. mc1r mutation, Arg65 - Cys - arginine at amino acid 65 changed to cysteine

      4. agouti protein produced by agouti gene

      5. agouti protein competes with MSH for access to mc1r

    4. why are gulf coast beach mice blond

      1. Arg65-Cys mutation in mc1r

    5. Is the coloration of the Atlantic coast beach mice due to the same ARg65Cys mutation found in the gulf coast beach mice?w

      1. no none of the Atlantic subspecies have the ArgCys mutation contributes to blond coloration

    6. why are Atlantic coast beach mice blond

      1. mc1r does not appear to be responsible for the blond coloration of atlantic coast beach mice

      2. a mutation in the enhancer region of agouti increased production of agouti protein in both atlantic and gulf coast populations

    7. why did blond fur evolve in beach mouse populations?

      1. blond mice suffer reduced predation by visual predators. with increased survival, blond beach mice are more likely to reproduce successfully and have higher evolutionary fitness than dark beach mice

    8. how did blond fur evolve in beach mouse populations

      1. proximate explanation #1

        1. a point mutation in the mc1r gene altered the protein code by that gene by one amino acid (Arg65-Cys) mc1r could no longer signal melanocytes to make eumelanin

      2. proximate explanation #2

        1. a mutation in the regulatory region of the agouti gene increased gene expression, producing more agouti protein. agouti binds to mc1r on the melanoctye membrane and prevents signaling to trigger eumalenin production

  8. Speciation

    1. allopatric

      1. intiated by geographic isolation

        1. dispersal

        2. vacariance

        3. extinction of populations in the center of the geographic range of a species

    2. sympatric

      1. speciation without the benefit of geographic isolation

        1. partitioning of resources and habitats

          1. disruptive selection

        2. autopolyploidy and allopolyploidy

  9. ensatina eschscholtzii

    1. an example of a ring species

    2. salamandars

      1. occupied all of northern and central california during the last ice age

      2. warming imposed a warm, dry environment in the central valley isolating salamanders in the coast range from those in the sierra nevadas